The present invention is generally directed to toner processes, and more specifically to aggregation and coalescence processes for the preparation of toner compositions. In embodiments, the present invention is directed to the economical preparation of toners without the utilization of the known pulverization and/or classification methods, and wherein toners with an average volume diameter of from about 1 to about 25, and preferably from 1 to about 10 microns and narrow GSD can be obtained. The resulting toners can be selected for known electrophotographic imaging and printing processes, including color processes, and lithography. In embodiments, the present invention is directed to a process comprised of dispersing a pigment and optionally a charge control agent or additive in an aqueous mixture containing an ionic surfactant in amount of from about 0.5 percent to about 10 percent and shearing this mixture with a latex mixture comprised of suspended resin particles of from about 0.01 micron to about 2 microns in volume average diameter in an aqueous solution containing a counterionic surfactant in amounts of from about 1 percent to about 10 percent with opposite charge to the ionic surfactant of the pigment dispersion, and nonionic surfactant in amount of from 0 percent to about 5 percent, thereby causing a flocculation of resin particles, pigment particles and optional charge control particles, followed by stirring of the flocculent mixture which is believed to form statically bound aggregates of from about 1 micron to about 10 microns, comprised of resin, pigment and optionally charge control particles, and thereafter, adding extra anionic or nonionic surfactant solution with a concentration of from about 5 percent to about 30 percent in the controlled amount, which will result in the overall final concentration of this surfactant in the aggregated mixture of from about 0.5 percent to about 10 percent, and preferably from 1 percent to 5 percent (weight percent throughout unless otherwise indicated) to thereby enable any further growth in particle size and GSD during the heating step, which size in embodiments is from about 3 to about 10 microns in average volume diameter, and with a GSD of from about 1.16 to about 1.26; and then heating the mixture above the polymeric resin Tg, which Tg is in range of from between about 45.degree. C. to about 90.degree. C. and preferably between about 50.degree. C. and 80.degree. C., and more preferably the resin Tg is equal to 54.degree. C., to generate toner with an average particle volume diameter of from about 1 to about 10 microns, and wherein the stirring speed in (iii) is reduced from about 300 to about 1,000 to about 100, preferably 150, to about 600 rpm, primarily to substantially eliminate fines of about 1 micron in average volume diameter, which fines can adversely affect toner yield. It is believed that during the heating stage, the components of aggregated particles fuse together to form composite toner particles. In another embodiment thereof, the present invention is directed to an in situ process comprised of first dispersing a pigment, such as HELIOGEN BLUE.sup..TM. or HOSTAPERM PINK.sup..TM., in an aqueous mixture containing a cationic surfactant, such as benzalkonium chloride (SANIZOL B-50.sup..TM.), utilizing a high shearing device, such as a Brinkmann Polytron, or microfluidizer or sonicator, thereafter shearing this mixture with a charged latex of suspended resin particles, such poly(styrene/butadiene/acrylic acid) or poly(styrene/butylacrylate/acrylic acid) or PLIOTONE.sup..TM. of poly(styrene butadiene), and of particle size ranging from about 0.01 to about 0.5 micron as measured by the Brookhaven nanosizer in an aqueous surfactant mixture containing an anionic surfactant, such as sodium dodecylbenzene sulfonate (for example NEOGEN R.sup..TM. or NEOGEN SC.sup..TM.) and nonionic surfactant, such as alkyl phenoxy poly(ethylenoxy) ethanol (for example IGEPAL 897.sup..TM. or ANTAROX 897.sup..TM.), thereby resulting in a flocculation, or heterocoagulation of the resin particles with the pigment particles; and which on further stirring for from about 1 hour to about 24 hours with optional heating at from about 5.degree. to about 25.degree. C. below the resin Tg, which Tg is in the range of between 45.degree. to 90 .degree. C. and preferably between about 50.degree. and 80.degree. C., results in formation of statically bound aggregates ranging in size of from about 0.5 micron to about 10 microns in average diameter size as measured by the Coulter Counter (Microsizer II); and adding concentrated (from about 5 percent to about 30 percent) aqueous surfactant solution containing an anionic surfactant, such as sodium dodecylbenzene sulfonate (for example NEOGEN R.sup..TM. or NEOGEN SC.sup..TM.) or nonionic surfactant such as alkyl phenoxy poly(ethylenoxy) ethanol (for example IGEPAL 897.sup..TM. or ANTAROX 897.sup..TM.), in controlled amounts to prevent any changes in particle size, which can range from 3 to 10 microns in average volume diameter and a GSD which can range from about 1.16 to about 1.28 during the heating step, and thereafter, heating to 10.degree. to 50.degree. C. above the resin Tg to provide for particle fusion or coalescence of the polymer and pigment particles; followed by washing with, for example, hot water to remove surfactants, and drying whereby toner particles comprised of resin and pigment with various particle size diameters can be obtained, such as from 1 to 12 microns in average volume particle diameter, and wherein the stirring speed in (iii) is reduced in (iv) as illustrated herein. The aforementioned toners are especially useful for the development of colored images with excellent line and solid resolution, and wherein substantially no background deposits are present. While not being desired to be limited by theory it is believed that the flocculation or heterocoagulation is formed by the neutralization of the pigment mixture containing the pigment and cationic surfactant absorbed on the pigment surface, with the resin mixture containing the resin particles and anionic surfactant absorbed on the resin particle. The high shearing stage disperses the large initially formed flocculants, and speeds up formation of stabilized aggregates negatively charged and comprised of the pigment and resin particles of about 0.5 to about 10 microns in volume diameter. Thereafter, extra or additional anionic surfactant percent, such as about 0.1 to about 5 weight based on the total weight of all components, can be added to increase the negative charge on the surface of the aggregated particles, thus increasing their stability, electrostatically, and preventing any further change in particle size (growth) of the aggregates during the heating stage, or coalescence step. Thereafter, heating is applied to fuse the aggregated particles or coalesce the particles to toner composites or particles comprising resin, pigment, and optional charge control agents (CCA). Furthermore, in other embodiments the ionic surfactants can be exchanged, such that the pigment mixture contains the pigment particle and anionic surfactant, and the suspended resin particle mixture contains the resin particles and cationic surfactant; followed by the ensuing steps as illustrated herein to enable flocculation by charge neutralization while shearing, and form statically bounded aggregate particles by stirring, stabilization of the above mentioned aggregate particles by addition of extra surfactant prior to heating, and toner formation after heating. Of importance with respect to the processes of the present invention in embodiments, in addition to reducing the stirring speeds, is controlling the amount of anionic or nonionic surfactant added to already formed aggregates to ensure, for example, that the dispersion of aggregated particles remains stable and thus can be effectively utilized in the coalescence process, and to enable the control of particle size in the coalescence step. More specifically, the method of formation of aggregated toner size particles from submicron size resin particles and submicron size pigment size results from these components being dispersed in oppositely charged surfactants, for example, the latex is a dispersion of polymeric particles in anionic surfactant, and the pigment can be dispersed in cationic surfactant. Aggregated particles are formed due to the partial charge neutralization of the surface of the latex particles, and aggregates, which are formed in the aggregation process, are negatively charged in embodiments and relatively stable, that is they are stable enough to withstand particle size measurements on the Coulter Counter, which requires addition of the electrolyte to perform the measurement, however, they may not be stable enough to withstand heating above the polymeric resin Tg, which is required to fuse resin and pigment particles together to form the toner composite. The addition of this extra portion of anionic or nonionic surfactant prior to heating increases the negative charge on the aggregated particles, thus enhancing the stability of the aggregated system to such an extent that the aggregated particles can retain their particle size and particle size distribution during the coalescence step. This can be important, especially for preparation of small toner composite particles, since one can control particle growth in the aggregation step and retain those particles through the heating stage. By adding extra anionic or nonionic surfactant to the already formed aggregated particles to stabilize the new colloidal system, either by electrosteric or steric stabilization, the system is of sufficient stability to withstand additional heating that is selected to coalesce the electrostatically bound aggregates. Without addition of this extra stabilizer, the particles may in embodiments have the tendency to further grow and multiply their size.
In reprographic technologies, such as xerographic and ionographic devices, toners with average volume diameter particle sizes of from about 9 microns to about 20 microns are effectively utilized. Moreover, in some xerographic technologies, such as the high volume Xerox Corporation 5090 copier-duplicator, high resolution characteristics and low image noise are highly desired, and can be attained utilizing the small sized toners of the present invention with an average volume particle of less than 11 microns and preferably less than about 7 microns, and with narrow geometric size distribution (GSD) of from about 1.16 to about 1.3. Additionally, in some xerographic systems wherein process color is utilized, such as pictorial color, small particle size colored toners of from about 3 to about 9 microns are highly desired to avoid paper curling. Paper curling is especially observed in pictorial or process color applications wherein three to four layers of toners are transferred and fused onto paper. During the fusing step, moisture is driven off from the paper because of the high fusing temperatures of from about 130.degree. to 160 .degree. C. applied to the paper from the fuser. Where only one layer of toner is present, such as in black or in highlight xerographic applications, the amount of moisture driven off during fusing is reabsorbed proportionally by paper, and the resulting print remains relatively flat with minimal curl. In pictorial color process applications wherein three to four colored toner layers are present, a thicker toner plastic level present after the fusing step inhibits the paper from sufficiently absorbing the moisture lost during the fusing step, and image paper curling results. These and other disadvantages and problems are avoided or minimized with the toners and processes of the present invention. It is preferable to use small toner particle sizes, such as from about 1 to 7 microns, and with higher pigment loading, such as from about 5 to about 12 percent by weight of toner, such that the mass of toner layers deposited onto paper is reduced to obtain the same quality of image, and resulting in a thinner plastic toner layer onto paper after fusing, thereby minimizing or avoiding paper curling. Toners prepared in accordance with the present invention enable the use of lower fusing temperatures, such as from about 120.degree. to about 150.degree. C., thereby avoiding or minimizing paper curl. Lower fusing temperatures minimize the loss of moisture from paper, thereby reducing or eliminating paper curl. Furthermore, in process color applications and especially in pictorial color applications, toner to paper gloss matching is highly desirable. Gloss matching is referred to as matching the gloss of the toner image to the gloss of the paper. For example, with a low gloss image of preferably from about 1 to about 30 gloss is preferred, low gloss paper is utilized, such as from about 1 to about 30 gloss units as measured by the Gardner Gloss metering unit, and which after image formation with small particle size toners of from about 3 to about 5 microns, and fixing thereafter results in a low gloss toner image of from about 1 to about 30 gloss units as measured by the Gardner Gloss metering unit. Alternatively, if higher image gloss is desired, such as from about above 30 to about 60 gloss units as measured by the Gardner Gloss metering unit, higher gloss paper is utilized, such as from about above 30 to about 60 gloss units, and which after image formation with small particle size toners of the present invention of from about 3 to about 5 microns, and fixing thereafter results in a higher gloss toner image of from about 30 to about 60 gloss units as measured by the Gardner Gloss metering unit. The aforementioned toner to paper matching can be attained with small particle size toners such as less than 7 microns and preferably less than 5 microns, such as from about 1 to about 4 microns such that the pile height of the toner layer(s) is low.
Numerous processes are known for the preparation of toners, such as, for example, conventional processes wherein a resin is melt kneaded or extruded with a pigment, micronized and pulverized to provide toner particles with an average volume particle diameter of from about 9 microns to about 20 microns and with broad geometric size distribution of from about 1.4 to about 1.7. In such processes, it is usually necessary to subject the aforementioned toners to a classification procedure such that a geometric size distribution of from about 1.2 to about 1.4 is attained. Also, in the aforementioned conventional process, low toner yields after classifications may be obtained. Generally, during the preparation of toners with average particle size diameters of from about 11 microns to about 15 microns, toner yields range from about 70 percent to about 85 percent after classification. Additionally, during the preparation of smaller sized toners with particle sizes of from about 7 microns to about 11 microns, lower toner yields are obtained after classification, such as from about 50 percent to about 70 percent. With the processes of the present invention in embodiments, small average particle sizes of from about 3 microns to about 9 microns, and preferably 5 microns are obtained without resorting to classification processes, and wherein narrow geometric size distributions are attained, such as from about 1.16 to about 1.30, and preferably from about 1.16 to about 1.25. High toner yields are also attained such as from about 90 percent to about 98 percent in embodiments. In addition, by the toner particle preparation process of this invention, small particle size toners of from about 3 microns to about 7 microns can be economically prepared in high yields, such as from about 90 percent to about 98 percent by weight based on the weight of all the toner material ingredients.
There is illustrated in U.S. Pat. No. 4,996,127 a toner of associated particles of secondary particles comprising primary particles of a polymer having acidic or basic polar groups and a coloring agent. The polymers selected for the toners of this '127 patent can be prepared by an emulsion polymerization method, see for example columns 4 and 5 of this patent. In column 7 of this '127 patent, it is indicated that the toner can be prepared by mixing the required amount of coloring agent and optional charge additive with an emulsion of the polymer having an acidic or basic polar group obtained by emulsion polymerization. Also, note column 9, lines 50 to 55, wherein a polar monomer, such as acrylic acid, in the emulsion resin is necessary, and toner preparation is not obtained without the use, for example, of acrylic acid polar group, see Comparative Example I. The process of the present invention need not utilize polymers with polar acid groups, and toners can be prepared with resins, such as poly(styrene-butadiene) or PLIOTONE.sup..TM., without containing polar acid groups. Additionally, the toner process of the '127 patent does not appear to utilize counterionic surfactant and flocculation. In U.S. Pat. No. 4,983,488, there is illustrated a process for the preparation of toners by the polymerization of a polymerizable monomer dispersed by emulsification in the presence of a colorant and/or a magnetic powder to prepare a principal resin component and then effecting coagulation of the resulting polymerization liquid in such a manner that the particles in the liquid after coagulation have diameters suitable for a toner. It is indicated in column 9 of this patent that coagulated particles of 1 to 100, and particularly 3 to 70, are obtained. This process is thus primarily directed to the use of coagulants, such as inorganic magnesium sulfate which results in the formation of particles with wide GSD. Furthermore, the '488 patent does not appear to disclose the process of counterionic flocculation. Similarly, the aforementioned disadvantages are noted in other prior art, such as U.S. Pat. No. 4,797,339, wherein there is disclosed a process for the preparation of toners by resin emulsion polymerization, wherein similar to the '127 patent polar resins of oppositely charges are selected, and wherein flocculation is not disclosed; and U.S. Pat. No. 4,558,108, wherein there is disclosed a process for the preparation of a copolymer of styrene and butadiene by specific suspension polymerization. Other patents mentioned are U.S. Pat. Nos. 3,674,736; 4,137,188 and 5,066,560.
In U.S. Pat. No. 5,290,654 (D/92277), the disclosure of which is totally incorporated herein by reference, there is disclosed a process for the preparation of toners comprised of dispersing a polymer solution comprised of an organic solvent, and a polyester and homogenizing and heating the mixture to remove the solvent and thereby form toner composites. Additionally, there is disclosed in U.S. Pat. No. 5,278,020 (D/92097), the disclosure of which is totally incorporated herein by reference, a process for the preparation of in situ toners comprising an halogenization procedure which, for example, chlorinates the outer surface of the toner and results in enhanced blocking properties.
In U.S. Pat. No. 5,308,734 (D/92576), the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toner compositions which comprises generating an aqueous dispersion of toner fines, ionic surfactant and nonionic surfactant, adding thereto a counterionic surfactant with a polarity opposite to that of said ionic surfactant, homogenizing and stirring said mixture, and heating to provide for coalescence of said toner fine particles.
In copending patent application U.S. Ser. No. 022,575 (D/92577), the disclosure of which is totally incorporated herein by reference there is disclosed a process for the preparation of toner compositions comprising
(i) preparing a pigment dispersion in a water, which dispersion is comprised of a pigment, an ionic surfactant, and optionally a charge control agent;
(ii) shearing the pigment dispersion with a latex mixture comprised of a counterionic surfactant with a charge polarity of opposite sign to that of said ionic surfactant, a nonionic surfactant and resin particles, thereby causing a flocculation or heterocoagulation of the formed particles of pigment, resin and charge control agent to form electrostatically bounded toner size aggregates; and
(iii) heating the statically bound aggregated particles to form said toner composition comprised of polymeric resin, pigment and optionally a charge control agent.
Disadvantages associated with some of the above processes, which disadvantages are avoided or minimized with the processes of the present invention, include preventing further growth in the size of the particles formed in the aggregation step during the heating of particles above their resin Tg, which is required to form stable toner composite particles. An advantage with the present process is that by the addition of extra surfactant as indicated herein one is able to retain the particle size distribution achieved in the aggregation step during the heating of particles above their resin Tg, which is needed to form stable toner composite particles. The primary advantage of accomplishing this is that one is able to control "by freezing" on to any given particle size and distribution, thus retaining these properties during the coalescence stage whereby the toner composites comprising resin pigment and optionally charge control agents are formed. Also, with the process of the present invention the stirring speed decrease enables controlled particle size and minimal further aggregation growth in (iv). This can increase the process latitude in controlling the particle size and particle size distribution.
In copending patent application U.S. Ser. No. 082,651 (D/93105), filed concurrently herewith, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toner compositions with controlled particle size comprising:
(i) preparing a pigment dispersion in water, which dispersion is comprised of pigment, an ionic surfactant and an optional charge control agent;
(ii) shearing at high speeds the pigment dispersion with a polymeric latex comprised of resin, a counterionic surfactant with a charge polarity of opposite sign to that of said ionic surfactant, and a nonionic surfactant thereby forming a uniform homogeneous blend dispersion comprised of resin, pigment, and optional charge agent;
(iii) heating the above sheared homogeneous blend below about the glass transition temperature (Tg) of the resin while continuously stirring to form electrostatically bound toner size aggregates with a narrow particle size distribution;
(iv) heating the statically bound aggregated particles above about the Tg of the resin particles to provide coalesced toner comprised of resin, pigment and optional charge control agent, and subsequently optionally accomplishing (v) and (vi);
(v) separating said toner; and
(vi) drying said toner.
In copending patent application U.S. Ser. No. 083,146 (D/93106), filed concurrently herewith, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toner compositions with a volume median particle size of from about 1 to about 25 microns, which process comprises:
(i) preparing by emulsion polymerization an anionic charged polymeric latex of submicron particle size, and comprised of resin particles and anionic surfactant;
(ii) preparing a dispersion in water, which dispersion is comprised of optional pigment, an effective amount of cationic flocculant surfactant, and optionally a charge control agent;
(iii) shearing the dispersion (ii) with said polymeric latex thereby causing a flocculation or heterocoagulation of the formed particles of optional pigment, resin and charge control agent to form a high viscosity gel in which solid particles are uniformly dispersed;
(iv) stirring the above gel comprised of latex particles, and oppositely charged dispersion particles for an effective period of time to form electrostatically bound relatively stable toner size aggregates with narrow particle size distribution; and
(v) heating the electrostatically bound aggregated particles at a temperature above the resin glass transition temperature (Tg) thereby providing said toner composition comprised of resin, optional pigment and optional charge control agent.
In copending patent application U.S. Ser. No. 082,741 (D/93108), filed concurrently herewith, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toner compositions with controlled particle size and selected morphology comprising
(i) preparing a pigment dispersion in water, which dispersion is comprised of pigment, ionic surfactant, and optionally a charge control agent;
(ii) shearing the pigment dispersion with a polymeric latex comprised of resin of submicron size, a counterionic surfactant with a charge polarity of opposite sign to that of said ionic surfactant and a nonionic surfactant thereby causing a flocculation or heterocoagulation of the formed particles of pigment, resin and charge control agent, and generating a uniform blend dispersion of solids of resin, pigment, and optional charge control agent in the water and surfactants;
(iii) (a) continuously stirring and heating the above sheared blend to form electrostatically bound toner size aggregates; or
(iii)(b) further shearing the above blend to form electrostatically bound well packed aggregates; or
(iii) (c) continuously shearing the above blend, while heating to form aggregated flake-like particles;
(iv) heating the above formed aggregated particles about above the Tg of the resin to provide coalesced particles of toner; and optionally
(v) separating said toner particles from water and surfactants; and
(vi) drying said toner particles.
In copending patent application U.S. Ser. No. 082,660 (D/93110), filed concurrently herewith, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toner compositions comprising:
(i) preparing a pigment dispersion, which dispersion is comprised of a pigment, an ionic surfactant, and optionally a charge control agent;
(ii) shearing said pigment dispersion with a latex or emulsion blend comprised of resin, a counterionic surfactant with a charge polarity of opposite sign to that of said ionic surfactant and a nonionic surfactant;
(iii) heating the above sheared blend below about the glass transition temperature (Tg) of the resin to form electrostatically bound toner size aggregates with a narrow particle size distribution; and
(iv) heating said bound aggregates above about the Tg of the resin.
In copending patent application U.S. Ser. No. 083,116 (D/93111), filed concurrently herewith, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toner compositions comprising
(i) preparing a pigment dispersion in water, which dispersion is comprised of pigment, a counterionic surfactant with a charge polarity of opposite sign to the anionic surfactant of (ii) and optionally a charge control agent;
(ii) shearing the pigment dispersion with a latex comprised of resin, anionic surfactant, nonionic surfactant, and water; and wherein the latex solids content, which solids are comprised of resin, is from about 50 weight percent to about 20 weight percent thereby causing a flocculation or heterocoagulation of the formed particles of pigment, resin and optional charge control agent; diluting with water to form a dispersion of total solids of from about 30 weight percent to 1 weight percent, which total solids are comprised of resin, pigment and optional charge control agent contained in a mixture of said nonionic, anionic and cationic surfactants;
(iii) heating the above sheared blend at a temperature of from about 5.degree. to about 25.degree. C. below about the glass transition temperature (Tg) of the resin while continuously stirring to form toner sized aggregates with a narrow size dispersity; and
(iv) heating the electrostatically bound aggregated particles at a temperature of from about 5.degree. to about 50.degree. C. above about the Tg of the resin to provide a toner composition comprised of resin, pigment and optionally a charge control agent.